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Replacing/Resealing Ductwork need help.

House built 1960, Charleston, SC - hot and humid
Brick ranch, 2300 sq/ft on crawlspace
Current ductwork is metal and located in crawlspace (not conditioned).
Replaced HVAC Unit 3 years ago - Carrier, 2 stage, 2 ton, located outside - does both heating and cooling.
Have 1 25x20 return.

I have hardwood floors throughout the house and no insulation underneath.

My termite guy was over doing an inspection and said I have problems with my HVAC. There is water beading up on the bottom of the floor boards above the main "trunk?" duct that runs down under the house. Why is this happening ? Also said the insulation is saturated with water.

Most of the other ducts are dripping and my mosture readings were really high.

Question is do I keep my metal ductwork and reseal it or do a complete rip-out and install another product? There is room to move around fairly well under there.

I have read about sealing existing ductwork with mastic...I have called the company that installed my HVAC unit...I think they are reputable. I just want some opinions on what my next steps should be.

Thanks for your reply. Just got done reading the other recent thread...with the guy that didn't accept the advice.

OK I am on board with the sealing the crawlspace and a dehum.

Questions: Would it be cheaper to keep my metal ductwork and rewrap it and seal with mastic or rip it out and put in another kind of duct. What is duct work is recommended for a sealed crawlspace in charleston, sc?

Thanks for your reply. Just got done reading the other recent thread...with the guy that didn't accept the advice.

OK I am on board with the sealing the crawlspace and a dehum.

Questions: Would it be cheaper to keep my metal ductwork and rewrap it and seal with mastic or rip it out and put in another kind of duct. What is duct work is recommended for a sealed crawlspace in charleston, sc?

Thanks - Ron

You should get someone BPI certified to come out and determine where your thermal barrier should be, either at the floors or at the walls & floor of your crawlspace itself. Since your ductwork is down there, it would be nice to have them inside the thermal envelope, but other considerations may make that impossible. If so, then you need an air seal & insulation on the underside of your floors. Then head off to the attic for similar work needed.

Would it be cheaper to keep my metal ductwork and rewrap it and seal with mastic or rip it out and put in another kind of duct.

Well, obviously it would be cheaper

The question to answer would be is the duct system designed properly. If it is, then by all means keep the metal duct. If its not designed adequately then maybe you should replace parts of it (with metal).

Try to find a duct system designer and get their opinion on if the layout is good. Being that its from 1960, it may not be. You probably at least need more returns.

Anyone here will tell you; ask me what time it is, and I'll tell you how to build a watch.

The moisture on the duct work is a result of humidity condensing on the cold metal surface. Any other condensation in the crawlspace is directly related to the damp environment, to which the condensation from the duct work is certainly contributing.

There are two solutions to your problem as I see it.

First, and probably best, since it will address the space as well as the duct is to insulate the perimeter of the crawl space. Eliminate any foundation vents that you may have, and insulate the interior surface of the crawlspace whether block or poured. By insulating the perimeter you create a 'conditioned space' and you prevent the infliltration of humidity. By doing this, you shouldn't have to insulate the duct work. If you are getting any seepage of ground water into the crawlspace, or the ground itself is damp, then you need to place a vapor barrier down on the ground as well.

If insulation of the crawlspace is not an option then you do need to insulate the duct work. This should help prevent the condensation from forming on the cold surface and dripping into the crawlspace. It is difficult under the best of circumstances to insulate properly duct that is already in place. Sort of like trying to thread a needle from across the room.

If the duct work has been damp over a period of time, I would replace the duct work with new insulated (either internally or externally) duct work. You don't want any exposed surfaces on which humidity could condense.

whoever you have perform the work, deal with a reputable licensed contractor for either the hvac or insulation work. (Your hvac contractor will address the insulation of the duct work). Once you have the work completed your system should operate at a more efficient level. At the time the duct work is replaced and insulated the contractor can verify the size is correct and make any necessary changes.

If you want to rewrap you first need to drop the metal trunk down to a workable level. If the trunk is still strapped to the floor joists you will never get a good tight seal and will have the same condensation

Contact Home Energy Group in Mt. Pleasant. They do BPI Training and testing. Note: you will have to pay them. Talk to Nancy St. Hilaire. They don't do the encapsulation, but probably know who does in that area. They ran a BPI class in my area that I just took this spring.

I don't think I am getting the right encapsulation install...Pls. Help...

Hi there - finally got around to getting an encapsulation done. They laid out the 10 mil vapor barrier throughout the crawl space. They ran it up the wall about 6" from the sill (?), folded it over and used a ramset to secure. The problem is two fold: they didn't seal the plastic to the brick. The piers run pretty close to the walls (3" or so) so here they just ran the plastic up the same 6" from the sill and secured - BUT I can put my hand down behind the pier and feel dirt (!) So the space is not really sealed - not sealed along the wall and not sealed behind piers. Question is, is this right? Should this be like an air-tight seal. Yes they are going to install a 90 pint dehumidifyer as well. What is the right way to do this in Charleston, SC?

Thanks!

Originally Posted by holyrail

House built 1960, Charleston, SC - hot and humid
Brick ranch, 2300 sq/ft on crawlspace
Current ductwork is metal and located in crawlspace (not conditioned).
Replaced HVAC Unit 3 years ago - Carrier, 2 stage, 2 ton, located outside - does both heating and cooling.
Have 1 25x20 return.

I have hardwood floors throughout the house and no insulation underneath.

My termite guy was over doing an inspection and said I have problems with my HVAC. There is water beading up on the bottom of the floor boards above the main "trunk?" duct that runs down under the house. Why is this happening ? Also said the insulation is saturated with water.

Most of the other ducts are dripping and my mosture readings were really high.

Question is do I keep my metal ductwork and reseal it or do a complete rip-out and install another product? There is room to move around fairly well under there.

I have read about sealing existing ductwork with mastic...I have called the company that installed my HVAC unit...I think they are reputable. I just want some opinions on what my next steps should be.